> It was working as designed and they didn't want to check less frequently, despite there being no logical reason to do this.

We had a similar thing, the other team wouldn't back down.

We ended up implementing a kind of rate limiting internally.

If the previous request (from that IP) was more than 4.5 seconds ago we let the check request through as normal.

If the previous request (from that IP) was more recent than that we just returned a cached "there is no update" payload that had a TTL of 60 seconds.

We told them this and left it up to them, they soon changed their polling frequency.

I'm surprised you were that nice about it. If it was that ridiculous I'd be reaching for fail2ban.